1. Field of the Invention
The invention relates generally to the field of digital amplifiers. More particularly, the invention relates to the processing of pulse modulated signals.
2. Discussion of the Related Art
Traditionally, audio amplifiers have operated in the analog domain. These amplifiers tend to have low power conversion efficiency, and consequently have large size and weight. With the advent of digital technology, particularly digital audio sources, audio amplification began being performed in the digital domain.
Digital audio amplifiers using pulse width modulation (PWM) have a higher power conversion efficiency than analog amplifiers, and have a fixed switched frequency. Unlike analog PWM, which quantizes using an analog ramp signal, or the like, digital PWM is quantized and generated by counting cycles of a high speed clock.
U.S. Pat. No. 6,414,613 to Midya, the disclosure of which is hereby expressly incorporated by reference, describes an integral noise shaping (INS) algorithm to quantize PWM waveforms. PWM noise shaping loops are used to improve the in-band signal-to-noise ratio (SNR) of quantized PWM signals by forcing the noise produced from quantizing a duty ratio signal to fall out of the frequency band of interest.
Pulse width modulation based switching amplifiers are often used in full bridge applications with four switches. In such applications, single-sided PWM processing can be utilized and the resulting signal then inverted to create the pair of signals necessary to drive the full bridge power stage. U.S. Pat. No. 6,414,613 is one such example.
To obtain high signal-to-noise ratio using the prior art, there are critical requirements for crystal reference clock frequency, output filtering, matching in the power stage, and matching in the signal path.